1. Field of the Invention
The present invention relates to a hydraulic braking device, and more particularly to a brake master cylinder that is conveniently assembled and having better sealing effect for hydraulic oil.
2. Description of the Related Art
A hydraulic brake apparatus utilized in a motorcycle or a bicycle can be taken as one of hydraulic equipment that is in widespread use. A brake master cylinder driven by a brake handlebar is disposed to a handgrip place of the hydraulic brake apparatus. In addition, a braking caliper is disposed to wheels through a hydraulic pipe. When a rider presses the brake handlebar, a piston relatively disposed in a main oil cylinder of the brake master cylinder is driven by the brake handlebar to go forward. Hydraulic oil within the main oil cylinder is pushed into a sub-oil cylinder of the braking caliper to allow a brake pad of the sub-oil cylinder to move toward the brake disc. The brake pad is in contact with the brake disc of the hub to further brake the wheels.
When the rider releases the brake handlebar, the piston in the main oil cylinder or the brake pad at the sub-oil cylinder can back off under the effect of the spring, and the brake handlebar can return to a predetermined angle.
Moreover, after performing braking motion for several times, the brake pad may be worn away (the brake pad is thinned). The reciprocation stroke of the piston must be relatively increased to achieve a desired braking effect. To avoid the brake handlebar from completely reciprocating due to the foregoing factors and to avoid influencing the braking force, an oil pot (or an oil cup) is further disposed to a normal brake master cylinder, and an oil-return hole connected to the oil pot is disposed to a reciprocation stroke place for the piston of the main oil cylinder.
With the state of completely backing the piston off, hydraulic oil within the oil pot is automatically filled into a hydraulic pipe in front of the piston through the oil-return hole. The brake handlebar may not return to a predetermined angle due to the abrasion of the brake pad, and the desired braking effect can be retained.
However, the conventional brake master cylinder usually disposes the oil pot at a radial position of the main oil cylinder of the handlebar base and must dispose a leakage prevention structure at the oil pot and a conjunction channel between the piston and the brake handlebar respectively to prevent hydraulic oil from being leaked. Consequently, it does not only influence the beauty of the brake master cylinder, but also increases the difficulty of assembling the brake master cylinder. Moreover, the sealing effect of hydraulic oil is relatively not good enough.
Therefore, no matter the brake master cylinder applied to the motorcycle or the bicycle has the function of automatically filling hydraulic oil or not, the reliability of the brake master cylinder can be greatly improved if the assembly convenience of the brake master cylinder and the sealing effect for hydraulic oil are actively improved and increased.